A light-emitting device including an organic EL element can be formed to have a planar shape, and the color of light emitted therefrom can be white or a color close to white. Therefore, it is contemplated that such light-emitting devices including organic EL elements are applicable as light sources of lighting devices for illuminating areas in living environments etc. or as backlight units of display devices.
However, the efficiency of currently known organic EL elements is insufficient for use in the aforementioned lighting applications. Therefore, it is desirable to improve the light extraction efficiency of organic EL elements. One known method for improving the light extraction efficiency of organic EL elements is to provide a variety of concavo-convex structures on the light-emitting surfaces of the organic EL elements. For example, there is a proposal in which a structure layer having a concavo-convex structure is provided on the light-emitting surface of an organic EL element (see Patent Literature 1). With this concavo-convex structure, light can be gathered in a favorable manner, and the light extraction efficiency can thereby be improved.
Techniques in Patent Literatures 2 and 3 are also known.